The present invention relates to a fuel injection system.
In internal combustion engines having spark ignition of a compressed fuel mixture with internal formation of the mixture, a xe2x80x9cmixture cloudxe2x80x9d, which must have a certain fuel-air ratio in the ignitable range, is required in an area of the spark plug for stratified charge operation. For this purpose, fuel injectors having nozzles that open toward the inside or the outside and produce a conical jet are used.
For example, German Published Patent Application No. 198 04 463 describes a fuel injection system for internal combustion engines having spark ignition of a compressed fuel mixture; this fuel injection system is provided with at least one fuel injector that injects fuel into a combustion chamber formed by a piston/cylinder arrangement and is equipped with a spark plug projecting into the combustion chamber. The nozzle body of the fuel injector is provided with at least one row of injection holes distributed over the circumference of a nozzle body of the fuel injector. Through controlled injection of fuel through the injection holes, a jet-guided combustion method is implemented by the formation of a mixture cloud, at least one jet being directed in the direction of the spark plug. Other jets ensure that an at least approximately closed, i.e., contiguous mixture cloud is formed.
German Published Patent Application No. 196 42 653 describes a method of forming an ignitable fuel-air mixture. An ignitable fuel-air mixture is formable in the cylinders of direct-injection internal combustion engines, in that fuel is injected into each combustion chamber delimited by a piston, by way of an injector on opening of a nozzle orifice due to a valve element being lifted up from a valve seat surrounding the nozzle orifice. To permit formation of an internal mixture optimized for fuel consumption and emissions at each operating point of the entire engine characteristics map under all operating conditions of the internal combustion engine, for example, in stratified charge operation, the opening stroke of the valve element and the injection time are adjustable.
German Published Patent Application No. 38 08 635 describes a fuel injection device for direct injection of fuel into the cylinder of an internal combustion engine having compression of a fuel mixture. The fuel injection device includes a fuel injector that is situated in the cylinder wall at a distance from the cylinder head and opposite the exhaust opening and has an outlet opening, with the axis of the jet of the injection valve being directed at the area around the spark plug situated in the cylinder head. The fuel injector has a magnetically operated valve needle having helical swirl grooves to produce a swirl flow of the injection jet. The total cross-sectional area of the swirl grooves is smaller by at least one half than the cross-sectional area of the outlet opening, the fuel injector being situated above a flushing opening, and with its jet axis directed at the ignition point situated at the center of the cylinder head.
Air-guided or wall-guided combustion methods are implemented with the injection systems described above. The air-guided combustion method depends to a very great extent on the movement of incoming air, which has the function of conveying an ignitable fuel-air mixture exactly into the electrode area of the spark plug over the entire stratified charge operation range of the engine characteristics map. In the wall-guided combustion method, fuel is carried to the spark plug with the support of more or less fractured combustion chamber geometries with simultaneous formation of the mixture.
Transport of the mixture to the spark plug is very incomplete in wall-guided and air-guided combustion methods in idling operation and in the lower partial load range. In the middle partial load range of operation, it is possible in part only with unjustifiably low manufacturing tolerances of the high-pressure injectors used or the flow guidance through the intake manifold. The inadequate reproducibility is apparent in particular in increased emission of unburned hydrocarbons due to isolated instances of misfiring.
On the other hand, the jet-guided combustion method is usable only above a certain cylinder stroke volume, which is approximately 500 cm3. A certain minimum size may be required for the hole diameter of the injection holes for technical reasons, so that the arrangements described above result in an overly rich mixture in the case of small cylinder stroke volumes. This results in inferior emission values and higher fuel consumption. The lower limit for the hole diameter is currently approximately 0.12 mm. The injection holes are created by the erosion method. The fuel volume injected can be reduced only by decreasing the number of injection holes, but then the geometry of the fuel jet may become less favorable for the flammability of the fuel-air mixture. Therefore, the fuel jet is aimed at the spark plug in these cases.
The fuel injection system according to the present invention may provide the advantage that due to an area remote from the spark plug being left out in injection, the quantity of fuel injected may be reduced by decreasing the number of injection holes without having to reduce the diameter of the injection holes. Thus, the requirements of a lower fuel demand of internal combustion engines having a small stroke may be taken into account without requiring complicated measures for introducing smaller injection holes into the fuel injector.
The thermal shock load and sooting of the spark plug may be reduced by tangential injection of fuel with respect to the position of the spark plug, so that the spray jets are not aimed directly at the spark plug.
The gap in the jet at the spark plug may permit an igniting of the fuel-air mixture during injection in all areas of the engine characteristics map and in all operating ranges of the internal combustion engine or to inject fuel during ignition.
Through a specific combination of the injection holes and thus the injection jets in the combustion chamber, the installed position of the intake and exhaust valves as well as of the spark plug in the cylinder head may also be taken into account, and the geometry of the combustion chamber depression in the piston may be utilized optimally.
Fuel injectors suitable for the fuel injection system may be manufactured inexpensively without requiring any additional manufacturing measures. In addition, sensitivity to the mounting depth of the spark plug may decrease due to the possible larger diameter of the injection holes.